Why is the Altaic hypothesis controversial among linguists?

The Altaic hypothesis, which proposes that Turkic, Mongolic, and Manchu-Tungus languages share a common genetic origin, remains a subject of significant debate among linguists.12

While some scholars argue that the group constitutes a valid language family based on systematic sound correspondences and structural similarities, many others contend that these commonalities are not sufficient to prove a genetic relationship. Critics of the hypothesis often attribute the shared features—such as similarities in vocabulary, morphology, and syntax—to prolonged geographic proximity and mutual influence rather than a common ancestor. This perspective views Altaic as an areal grouping rather than a genetic one.12

Furthermore, attempts to expand the hypothesis to include Korean and Japanese have faced additional skepticism. While some researchers find the evidence for a link with Korean compelling, the inclusion of Japanese is generally regarded as highly speculative. Consequently, because the available evidence has not led to a scholarly consensus, the status of the Altaic group continues to be viewed as a hypothesis that is difficult to demonstrate definitively.1